Dummy metal with zigzagged edges

ABSTRACT

A structure includes a metal pad, a passivation layer having a portion covering edge portions of the metal pad, and a dummy metal plate over the passivation layer. The dummy metal plate has a plurality of through-openings therein. The dummy metal plate has a zigzagged edge. A dielectric layer has a first portion overlying the dummy metal plate, second portions filling the first plurality of through-openings, and a third portion contacting the first zigzagged edge.

BACKGROUND

In the formation of integrated circuits, devices such as transistors areformed at the surface of a semiconductor substrate in a wafer. Aninterconnect structure is then formed over the integrated circuitdevices. A metal pad is formed over, and is electrically coupled to, theinterconnect structure. A passivation layer and a first polymer layerare formed over the metal pad, with the metal pad exposed through theopenings in the passivation layer and the first polymer layer.

Post-passivation interconnect (PPI) is then formed, followed by theformation of a second polymer layer over the PPI. AnUnder-Bump-Metallurgy (UBM) is formed extending into an opening in thesecond polymer layer, wherein the UBM is electrically connected to thePPI. A solder ball is then placed over the UBM and reflowed.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a cross-sectional view of a portion of a wafer inaccordance with some exemplary embodiments, wherein the wafer includes aPost-Passivation Interconnect (PPI) having a dummy metal plate inaccordance with some embodiments.

FIGS. 2 through 6 are top views of dummy metal plates in accordance withsome embodiments.

FIGS. 7 and 8 illustrate the top views of dummy metal plates in a wholechip in accordance with some embodiments.

FIG. 9 illustrate a top view of large dummy metal plates with zigzaggededges and small dummy metal plates with smooth edges.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “underlying,” “below,”“lower,” “overlying,” “upper” and the like, may be used herein for easeof description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. Thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. The apparatus may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

A dummy metal in a redistribution layer of a die (or a wafer) isprovided in accordance with various exemplary embodiments. Somevariations of some embodiments are discussed. Throughout the variousviews and illustrative embodiments, like reference numbers are used todesignate like elements.

FIG. 1 illustrates a cross-sectional view of package component 2. Inaccordance with some embodiments of the present disclosure, packagecomponent 2 is a device wafer including active devices such astransistors and/or diodes, and possibly passive devices such ascapacitors, inductors, resistors, or the like. In accordance withalternative embodiments of the present disclosure, package component 2is an interposer wafer, which may or may not include active devicesand/or passive devices. In accordance with yet alternative embodimentsof the present disclosure, package component 2 is a package substratestrip, which includes core-less package substrates or the packagesubstrates with cores therein. In subsequent discussion, a device waferis discussed as an exemplary package component 2. The teaching of thepresent disclosure may also be applied to interposer wafers, packagesubstrates, etc.

In accordance with some embodiments of the present disclosure, theexemplary wafer 2 includes semiconductor substrate 20 and the featuresformed at a top surface of semiconductor substrate 20. Semiconductorsubstrate 20 may comprise crystalline silicon, crystalline germanium,silicon germanium, and/or a III-V compound semiconductor such as GaAsP,AlInAs, AlGaAs, GaInAs, GaInP, GaInAsP, and the like. Semiconductorsubstrate 20 may also be a bulk silicon substrate or aSilicon-On-Insulator (SOI) substrate. Shallow Trench Isolation (STI)regions (not shown) may be formed in semiconductor substrate 12 toisolate the active regions in semiconductor substrate 20. Although notshown, through-vias may be formed to extend into semiconductor substrate20, wherein the through-vias are used to electrically inter-couple thefeatures on opposite sides of wafer 2.

In accordance with some embodiments of the present disclosure, wafer 2includes integrated circuit devices 22, which are formed on the topsurface of semiconductor substrate 20. Exemplary integrated circuitdevices 22 include Complementary Metal-Oxide Semiconductor (CMOS)transistors, resistors, capacitors, diodes, and the like. The details ofintegrated circuit devices 22 are not illustrated herein. In accordancewith alternative embodiments, wafer 2 is used for forming interposers,wherein substrate 20 may be a semiconductor substrate or a dielectricsubstrate.

Inter-Layer Dielectric (ILD) 24 is formed over semiconductor substrate20 and fills the space between the gate stacks of transistors (notshown) in integrated circuit devices 22. In accordance with someexemplary embodiments, ILD 24 comprises phosphosilicate glass (PSG),borosilicate glass (BSG), boron-doped phosphosilicate glass (BPSG),fluorine-doped silicate glass (FSG), tetraethyl orthosilicate (TEOS), orthe like. ILD 24 may be formed using spin coating, Flowable ChemicalVapor Deposition (FCVD), or the like. In accordance with alternativeembodiments of the present disclosure, ILD 24 is formed using adeposition method such as Plasma Enhanced Chemical Vapor Deposition(PECVD), Low Pressure Chemical Vapor Deposition (LPCVD), or the like.

Contact plugs 28 are formed in ILD 24, and are used to electricallyconnect integrated circuit devices 22 to overlying metal lines, andvias. In accordance with some embodiments of the present disclosure,contact plugs 28 are formed of a conductive material selected fromtungsten, aluminum, copper, titanium, tantalum, titanium nitride,tantalum nitride, alloys therefore, and/or multi-layers thereof. Theformation of contact plugs 28 may include forming contact openings inILD 24, filling a conductive material(s) into the contact openings, andperforming a planarization (such as Chemical Mechanical Polish (CMP)) tolevel the top surfaces of contact plugs 28 with the top surface of ILD24.

Over ILD and contact plugs 28 is interconnect structure 30. Interconnectstructure 30 includes metal lines 34 and vias 36, which are formed indielectric layers 32. The combination of metal lines at a same level isreferred to as a metal layer hereinafter. In accordance with someembodiments of the present disclosure, interconnect structure 30includes a plurality of metal layers that are interconnected throughvias 36. Metal lines 34 and vias 36 may be formed of copper or copperalloys, and they can also be formed of other metals. In accordance withsome embodiments of the present disclosure, dielectric layers 32 areformed of low-k dielectric materials. The dielectric constants (kvalues) of the low-k dielectric materials may be less than about 3.0, orless than about 2.5, for example.

Dielectric layers 32 are alternatively referred to as Inter-MetalDielectric (IMD) layer 32 hereinafter. In accordance with someembodiments of the present disclosure, IMD layers 32 are formed of alow-k dielectric material having a dielectric constant (k-value) lowerthan about 3.0, about 2.5, or even lower. IMD layers 32 may compriseBlack Diamond (a registered trademark of Applied Materials), acarbon-containing low-k dielectric material, Hydrogen SilsesQuioxane(HSQ), MethylSilsesQuioxane (MSQ), or the like. IMD layers 32 may alsohave a low-k value, which may be lower than about 3.0, 2.5, or 2.0. Inaccordance with some embodiments of the present disclosure, theformation of IMD layers 32 includes depositing a porogen-containingdielectric material and then performing a curing process to drive outthe porogen, and hence the remaining IMD layers 32 is porous.

Metal lines 34 and vias 36 are formed in IMD layers 32. The formationprocess may include single damascene and dual damascene processes. In anexemplary single damascene process, a trench is first formed in one ofIMD layers 32, followed by filling the trench with a conductivematerial. A planarization such as CMP is then performed to remove theexcess portions of the conductive material higher than the top surfaceof the IMD layer, leaving a metal line in the trench. In a dualdamascene process, both a trench and a via opening are formed in an IMDlayer, with the via opening underlying and connected to the trench. Theconductive material is then filled into the trench and the via openingto form a metal line and a via respectively. The conductive material mayinclude a diffusion barrier layer and a copper-containing metallicmaterial over the diffusion barrier layer, wherein the barrier layer mayinclude titanium, titanium nitride, tantalum, tantalum nitride, or thelike.

Passivation layer 40 (sometimes referred to as passivation-1) may beformed over interconnect structure 30, wherein vias 44 are formed inpassivation layer 40 to electrically connect metal lines 34 and vias 36to overlying metal pads 42.

Metal pads 42 are formed over passivation layer 40, and may beelectrically coupled to integrated circuit devices 22 through vias 44 inpassivation layer 40, and through metal lines 34 and vias 36 inaccordance with some exemplary embodiments. Metal pads 42 may bealuminum pads or aluminum-copper pads, and other metallic materials maybe used.

Passivation layer 46 (sometimes referred to as passivation-2) is formedover passivation layer 40. Some portions of passivation layer 46 maycover the edge portions of metal pads 42, and central portions of metalpads 42 are exposed through openings in passivation layer 46. Each ofpassivation layers 40 and 46 may be a single layer or a composite layer,and may be formed of a non-porous material. In accordance with someembodiments of the present disclosure, one or both of passivation layers40 and 46 is a composite layer comprising a silicon oxide layer (notshown), and a silicon nitride layer (not shown) over the silicon oxidelayer. Passivation layers 40 and 46 may also be formed of othernon-porous dielectric materials such as Un-doped Silicate Glass (USG),silicon oxynitride, and/or the like.

Polymer layer 48 is formed over passivation layer 46. Polymer layer 48may comprise a polymer such as polyimide, PolyBenzOxazole (PBO),BenzoCycloButene (BCB), or the like. The formation methods may includespin coating, for example. Polymer layer 48 may be dispensed in a liquidform, and then cured.

Polymer layer 48 is patterned, and PPIs 50 and dummy metal plates 100and 200 are formed, which include first portions overlying polymer layer48, and second portions extending into polymer layer 48 to electricallycouple to metal pads 42. The term “PPI” indicates that the formation ofPPIs 50 is after the formation of passivation layer 46. In accordancewith some embodiments of the present disclosure, the formation of PPIs50 and dummy metal plates 100 and 200 includes depositing a seed layer(not shown), forming and patterning a mask layer (such as photo resist,not shown) over the seed layer, and then plating a metal layer over theseed layer and in the openings of the mask layer. The seed layer mayinclude a titanium layer and a copper layer over the titanium layer, andmay be deposited using Physical Vapor Deposition (PVD). The metal layermay be formed of pure copper, substantially pure copper, or a copperalloy, and may be formed using plating. After the formation of the metallayer, the mask layer is removed. An etching step is performed to removethe portions of the seed layer underlying the removed mask layer.

FIG. 1 also illustrates the formation of polymer layer 52 andUnder-Bump-Metallurgies (UBMs) 54. Polymer layer 52 may comprisepolyimide or other polymer-based material such as PBO or BCB. Inaccordance with some embodiments of the present disclosure, polymerlayer 52 is formed using spin coating. Polymer layer 52 comprises someportions overlapping PPIs 50.

UBM layers 54 are formed to electrically couple to PPIs 50. Inaccordance with some embodiments of the present disclosure, each of UBMlayers 54 includes a barrier layer and a metal layer (not shown) overthe barrier layer. UBM layers 54 extend into the opening in polymerlayer 52, and are electrically coupled to, and may be in physicalcontact with, PPIs 50. The barrier layer may be a titanium layer, atitanium nitride layer, a tantalum layer, a tantalum nitride layer, or alayer formed of a titanium alloy or a tantalum alloy.

Electrical connectors 56 are formed over UBM layers 54. In accordancewith some embodiments of the present disclosure, electrical connectors56 are metal regions, which are either solder balls placed on UBM layers54, or non-solder metal pillars formed on UBM layers 54 through plating.In the embodiments wherein solder balls are used, the solder balls maygo through a reflow process to form solder regions. In accordance withalternative embodiments, electrical connectors 56 comprise metalpillars, which may be copper pillars. Additional layers such as a nickellayer, a solder cap, a palladium layer, and/or the like, may also beformed on each of the metal pillars.

Wafer 2 will be singulated as a plurality of dies 10, wherein each ofthe dies 10 includes the structures including substrate 20, interconnectstructure 30, metal pads 42, PPIs 50, dummy metal plates 100 and 200,and electrical connectors 56.

FIG. 2 illustrates a top view of the dummy metal pads 100 and 200. Theexemplary dummy metal plates 100 and 200 are also illustrated in FIG. 1.In accordance with some embodiments of the present disclosure, dummymetal plates 100 and 200 are formed simultaneously as the formation ofPPIs 50. Accordingly, dummy metal plates 100 and 200 are formed of thesame material as PPIs 50. Dummy metal plate 100 and dummy metal plate200 are physically spaced apart from each other by spacing C, which maybe greater than about 10 μm in accordance with some embodiments. SpacingC is filled with a dielectric material such as polymer layer 52 as shownin FIG. 1.

Each of dummy metal plates 100 and 200 is a continuous metal pad, with aplurality of through-openings 112 in each of dummy metal plates 100 and200. Openings 112 may have a repeated pattern such as an array. Openings112 are filled with a dielectric material such as polymer layer 52 asshown in FIG. 1. By forming openings 112 in dummy metal plates 100 and200, the metal pattern density of dummy metal plates 100 and 200 isreduced, and hence in the formation of PPIs 50 as shown in FIG. 1, thepattern-loading effect caused by non-uniform metal pattern density isreduced. The top-view shape of openings 112 may be rectangles, circles,hexagons, octagons, ellipses, or the like. An exemplary PPI 50 isillustrated as encircled by dummy metal plate 100. It is noted thatthere may be a plurality of PPIs 50 encircled by dummy metal plate 100,and there may be one or a plurality of PPIs 50 encircled by dummy metalplate 200 also. Dummy metal plates 100 and 200 may be electricallyconnected to the electrical ground, or may be electrically floating. Inaccordance with some embodiments, dummy metal plates 100 and 200 areconnected to one of electrical connectors 56 (FIG. 1) that is used forgrounding through some PPIs 50.

Dummy metal plate 100 has bent (zigzagged) edge 102, and dummy metalplate 200 has bent (zigzagged) edge 202. Edges 102 and 202 face eachother, and may be parallel with each other. Throughout the description,when edges 102 and 202 are referred to as parallel to each other, itindicates that the plurality of sections of edges 102 is parallel to thenearest sections of edges 202. Furthermore, the respective sections ofedges 102 and 202 may be, or may not be, spaced apart from each other byuniform spacing C.

In accordance with the embodiments of the present disclosure, edge 102,instead of being a long and straight edge, is bent (zigzagged), and haveneighboring sections that are short and extend in different directions(such as X-direction, Y-direction, or other directions as shown in FIGS.4 through 6). It is appreciated that if dummy metal plates 100 and 200have long and straight edges, during thermal cycles, since an entirelong edge contracts or expands in the same direction, which isperpendicular to the lengthwise direction of the respective edge, theaccumulated contracting or expanding force may cause crack to be formedalong the interface between the edge and the contacting dielectricmaterial. On the other hand, when the long and straight edges areredesigned as having short sections that extend in different directions,since the contracting or expanding force of each of the sections isperpendicular to the lengthwise direction of the respective section, theforces are much smaller and are in different directions. The stressvector at the interface of metal dummy plates and the dielectricmaterial is thus discontinued, and the likelihood of generating cracksis reduced.

Referring back to FIG. 2, the edge sections, regardless of theirextending directions, are designed to have lengths smaller than athreshold length. In accordance with some exemplary embodiments, thethreshold length is about 400 μm. Experiment results indicated that alarge metal pad with all of its edge sections being smaller than about400 μm will not have the cracks generated along their edges duringthermal cycles, while if the large metal pads have long edges areformed, cracks were observed.

FIG. 2 illustrates dummy metal plate 100 has protruding portions 104,and length A and width D of protruding portions 104 are smaller than thethreshold length such as 400 μm. Furthermore, dummy metal plate 100 hasrecesses 106, and the respective sections of edge 102 are recessed withrelative to its neighboring edge sections. The length and width ofrecesses 106 are also smaller than the threshold length. Similarly, edge202 of dummy metal plate 200 also includes a plurality of edge sections,with neighboring edge sections extending in different directions.Furthermore, the lengths of the edge sections of edge 202 are alsosmaller than the threshold length.

The bent edges 102 and 202 may form zigzag patterns. FIG. 2 illustratesa small portion of dummy metal plates 100 and 200, and the zigzagpattern may repeat. The number of repeating is determined by the overalllength of edges 102 and 202, and may be any number greater than 1. Forexample, the edge portions including a protruding portion 104 and arecess 106 may form a base unit that is repeated. Protruding portions104 and recesses 106 may be laid out in an alternating pattern.Furthermore, protruding portions 104 in the repeated patterns may havethe same length and/or the same width, and recesses 106 may have thesame length and/or the same width.

Dummy metal plate 200 may have a portion 204 protruding toward recess106. Protruding portion 204 may also have a portion extending intorecess 106. Similarly, dummy metal plate 100 may have protruding portionprotruding toward, and possibly extending into, recess 206 of dummymetal plate 200.

In accordance with some embodiments of the present disclosure, thezigzagged edges are adopted when the respective edges of a dummy metalpad are long, for example, when lengths E or F is longer than 400 μm, inwhich case, the stress vector is high enough to crack the dielectric(polymers 48 and/or 52 in FIG. 1). If the respective edge is alreadyshort, then the edge may be left being straight without being bent. Forexample, FIG. 9 illustrates dummy metal plates 300 with length E′smaller than length E, wherein length E′ is smaller than the thresholdlength, which may be smaller than about 400 μm. Accordingly, the edgesof dummy metal plates 300 are left as straight, and are not bent(zigzagged).

In accordance with some embodiments of the present disclosure,throughout the entire wafer 2 and the entire die 10 (FIG. 1), allstraight edges of dummy metal plates that are longer than the thresholdlength are bent, so that the straight sections of the bent edgesthroughout wafer 2 (and die 10) are equal to or smaller than thethreshold length. Alternative stated, no dummy metal plate in wafer 2has straight edge that is longer than the threshold length. To achievesuch as design, an integrated circuit design process in accordance withthe embodiments of the present disclosure may include designing theinitial pattern of dummy metal plates, predetermining a thresholdlength, searching for any edge of dummy metal plates that is longer thanthe threshold length, and modify the design to bend the edge intostraight and short sections, with none of the straight sections havinglength greater than the threshold length. During the modification of thedesign, the edges of the dummy metal plates that are equal to or shorterthan the threshold length may be kept unmodified.

FIGS. 3 through 6 illustrate the top views of dummy metal plates 100 and200 in accordance with some embodiments of the present disclosure,wherein the discussion of the dummy metal pads 100 and 200 in FIG. 2,whenever applicable, also applies to the embodiments in FIGS. 3 through6. It is noted that each of FIGS. 3 through 6 illustrate small portionsof dummy metal plates 100 and 200, and the illustrated patterns of edgesections may be repeated to have zigzag patterns. Referring to FIG. 3,in accordance with some embodiments of the present disclosure, recess108 of dummy metal plate 100 is further recessed from recess 106.Accordingly, protruding portion 210 of dummy metal plate 200 may furtherprotrude beyond protruding portion 204. In these embodiments, whenrecesses 106 and 108 are in combination considered as a compositerecess, the illustrated edge 102 has a protruding portion and a recessnext to the protruding portion. The protruding portion and the recessmay be repeated, and hence the edge 102 of dummy metal plate 100 alsohas a zigzag pattern. Similarly, edge 202 of dummy metal plate 200 alsohas a zigzag pattern. Furthermore, the protruding portions of dummymetal plate 100 may extend toward, and possibly into, the recess ofdummy metal plate 200, and vice versa.

In the exemplary embodiments as shown in FIGS. 2 and 3, the neighboringsections of edges 102 and 202 are perpendicular to each other to formright angles. FIGS. 4, 5, and 6 illustrate some exemplary embodiments inwhich the outer angles (the angles measured outside of dummy metalplates 100 and 200) are obtuse angles, which are greater than 90degrees. As a result, the protruding portions 104 and 204 may havetrapezoid shapes. Experiment results indicate that acute angles are morelikely to cause cracking in dummy metal plates, and acute angles andright angles result in more reliable dielectric layer and dummy metalplate that do not crack. In accordance with some exemplary embodiments,outer angle θ is about 135 degrees.

FIG. 5 illustrates an exemplary embodiment wherein the edge sections onopposite sides of a protruding portion of a dummy metal plate are notaligned to a straight line. For example, edge sections 202A and 202B arealigned to straight lines 212 and 214, respectively, which do notoverlap. Accordingly, edges 202C and 202D of protruding portion 204 havedifferent lengths. Correspondingly, the edge sections 102A and 102B,which are on the opposite sides of recess 106, are not aligned to astraight line.

FIG. 6 illustrates yet other dummy metal plates 100 and 200 inaccordance with some embodiments, wherein the edges on opposite sides ofprotruding portion 204 have different number of sections. For example, asingle section 204A forms one edge of protruding portion 204, whilesections 204B, 204C, and 204D in combination form the opposite edge ofprotruding portion 204.

FIG. 7 illustrates dummy metal plates 100 and 200 in die 10 inaccordance with some exemplary embodiments. Dummy metal plate 200 mayfully encircle dummy metal plate 100, with spacing C separating dummymetal plates 100 and 200 from each other. Dashed rectangles 58 are drawnto represent some regions of die 10, wherein the magnified views ofregions 58 may be represented by FIGS. 2 through 6 in any combination.The openings 112 and PPIs 50 (FIGS. 2 through 6) are not illustrated inFIG. 7, although they still exist in dummy metal plates 100 and/or 200in FIG. 7. In these embodiments, dummy metal plate 100 includes fouredges 102, which, when magnified as shown in FIGS. 2 through 6, are bentand have zigzag patterns. Furthermore, dummy metal plate 200 includesfour edges 202, which, when magnified, are also zigzagged as shown inFIGS. 2 through 6. Dummy metal plate 200 may also include four edges 222proximal the edges of die 10. Edges 222, when magnified, are alsozigzagged as shown in FIGS. 2 through 6.

FIG. 8 illustrates dummy metal plates 100, 200, and 400 in die 10 inaccordance with some exemplary embodiments. Dummy metal plates 100, 200,and 400 have irregular top-view shapes in accordance with someembodiments. Dummy metal plates 100, 200, and 400 are spaced apart fromeach other by a dielectric material. Dashed regions 58 are drawn,wherein the magnified views of regions 58 may be represented by FIGS. 2through 6 in any combinations. The openings 112 and PPIs 50 (FIGS. 2through 6) are not illustrated, although they still exist in dummy metalplates 100 and/or 200 in FIG. 8. In these embodiments, edges 102 ofdummy metal plate 100, edges 202 of dummy metal plate 200, and edges 402of dummy metal plate 400, when magnified as shown in FIGS. 2 through 6,are also bent/zigzagged.

Referring back to FIG. 1, one PPI layer that includes PPIs 50 and dummymetal plates 100 and 200 is shown in accordance with some embodiments.In accordance with alternative embodiments, there may be two, three, ormore PPI layers over the illustrated PPI layer. In the overlying PPIlayers, there may be dummy metal plates similar to dummy metal plates100, 200, 300, and 400 as illustrated in FIGS. 2 through 8. The patternsand the edge design of the dummy metal plates in the overlying PPIlayers are essentially the same as presented in the embodiments of thepresent disclosure, and hence are not repeated.

The embodiments of the present disclosure have some advantageousfeatures. By replacing the long straight edges of the dummy metal plateswith short straight edges extending in different directions, the stresson the otherwise long straight edges is discontinued, and cracks areless likely to occur.

In accordance with some embodiments of the present disclosure, astructure includes a metal pad, a passivation layer having a portioncovering edge portions of the metal pad, and a dummy metal plate overthe passivation layer. The dummy metal plate has a plurality ofthrough-openings therein. The dummy metal plate has a zigzagged edge. Adielectric layer has a first portion overlying the dummy metal plate,second portions filling the first plurality of through-openings, and athird portion contacting the first zigzagged edge.

In accordance with some embodiments of the present disclosure, astructure includes a first dummy metal plate having a first plurality ofprotrusions and a first plurality of recesses located alternatively. Thestructure further includes a second dummy metal plate having a secondplurality of protrusions and a second plurality of recesses locatedalternatively. A polymer strip separates the first dummy metal platefrom the second dummy metal plate, wherein opposite edges of the polymerstrip are in contact with the first dummy metal plate from the seconddummy metal plate.

In accordance with some embodiments of the present disclosure, a dieincludes a first dummy metal plate having a first plurality ofprotrusions and a first plurality of recesses located in a firstalternating layout, and a second dummy metal plate fully encircling thefirst dummy metal plate. The second dummy metal plate has a secondplurality of protrusions and a second plurality of recesses located in asecond alternating layout. The first plurality of protrusions extendsinto corresponding ones of the second plurality of recesses, and thesecond plurality of protrusions extends into corresponding ones of thefirst plurality of recesses. A dielectric layer separates the firstdummy metal plate from the second dummy metal plate.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A structure comprising: a metal pad; apassivation layer having a portion covering edge portions of the metalpad; a first dummy metal plate over the passivation layer, wherein thefirst dummy metal plate has a first plurality of through-openingstherein, and the first dummy metal plate comprises a first zigzaggededge; and a dielectric layer comprising: a first portion overlying thefirst dummy metal plate; second portions filling the first plurality ofthrough-openings; and a third portion contacting the first zigzaggededge.
 2. The structure of claim 1, wherein the first zigzagged edgecomprises a plurality of edge portions, with neighboring ones of theplurality of edge portions extending in different directions, andwherein none of the edge portions of the first zigzagged edge has alength greater than about 400 μm.
 3. The structure of claim 1, whereinthe first dummy metal plate comprises first protrusions and firstrecesses, with the first zigzagged edge comprising edges of the firstprotrusions and the first recesses, and the first protrusions and thefirst recesses are allocated in an alternating pattern.
 4. The structureof claim 3, wherein the first protrusions have a first same width and afirst same length as each other, and the first recesses have a secondsame width and a second same length as each other.
 5. The structure ofclaim 3, wherein the first protrusions have trapezoid top-view shapes.6. The structure of claim 3 further comprising a second dummy metalplate over the passivation layer, wherein the second dummy metal platecomprises a second zigzagged edge with second protrusions and secondrecesses, and the first protrusions extend into corresponding ones ofthe second recesses, and the second protrusions extend intocorresponding ones of the first recesses.
 7. The structure of claim 1further comprising a second dummy metal plate over the passivationlayer, wherein the second dummy metal plate has a second plurality ofthrough-openings therein, and the second dummy metal plate comprises asecond zigzagged edge with a plurality of sections, with the firstzigzagged edge and the second zigzagged edge having a substantiallyuniform spacing therebetween.
 8. The structure of claim 7, wherein thefirst zigzagged edge comprises an additional plurality of sections,wherein the additional plurality of sections is parallel to respectiveones of the plurality of sections of the second zigzagged edge.
 9. Thestructure of claim 1 further comprising a redistribution line fullyencircled by the first dummy metal plate.
 10. A structure comprising: afirst dummy metal plate comprising: a first plurality of protrusions anda first plurality of recesses located alternatively; a second dummymetal plate comprising: a second plurality of protrusions and a secondplurality of recesses located alternatively; and a polymer stripseparating the first dummy metal plate from the second dummy metalplate, wherein opposite edges of the polymer strip are in contact withthe first dummy metal plate from the second dummy metal plate.
 11. Thestructure of claim 10, wherein the first plurality of protrusions haslengths equal to each other, and the first plurality of recesses havewidths equal to each other.
 12. The structure of claim 10, wherein thefirst dummy metal plate comprises a first edge having a first pluralityof edge sections, and the second dummy metal plate comprises a secondedge having a second plurality of edge sections, and each of the firstplurality of edge sections is parallel to a corresponding nearest one ofthe second plurality of edge sections.
 13. The structure of claim 10,wherein the first dummy metal plate fully encircles the second dummymetal plate.
 14. The structure of claim 10, wherein each of the firstplurality of protrusions extends into a corresponding one of the secondplurality of recesses, and each of the second plurality of protrusionsextends into a corresponding one of the first plurality of recesses. 15.The structure of claim 10, wherein the first plurality of protrusionsand the first plurality of recesses have trapezoid top-view shapes. 16.The structure of claim 10, wherein the first plurality of protrusionsand the first plurality of recesses have rectangular top-view shapes.17. A structure comprising: a die comprising: a first dummy metal platecomprising a first plurality of protrusions and a first plurality ofrecesses located in a first alternating layout; a second dummy metalplate fully encircling the first dummy metal plate, wherein the seconddummy metal plate comprises a second plurality of protrusions and asecond plurality of recesses located in a second alternating layout,wherein the first plurality of protrusions extends into correspondingones of the second plurality of recesses, and the second plurality ofprotrusions extends into corresponding ones of the first plurality ofrecesses; and a dielectric layer separating the first dummy metal platefrom the second dummy metal plate.
 18. The structure of claim 17,wherein the second dummy metal plate comprises outer edges proximal torespective edges of the die.
 19. The structure of claim 18, wherein theouter edges of the second dummy metal plate are zigzagged.
 20. Thestructure of claim 17, wherein the first dummy metal plate and thesecond dummy metal plate are electrically grounded.